<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
    <title>simple</title>
    <style>
      .li {
        background-color: red;
        width: 40px;
        height: 40px;
      }
      .ul > .li {
        width: 80px;
      }
    </style>
  </head>
  <body>
    <div class="ul">
      <!-- <div> -->
      <div class="li">xxx</div>
      <div>yyyy</div>
      <!-- </div> -->
    </div>
    <div class="li">zzzz</div>
    <div class="simple">
      <!-- <div class="before"></div> -->

      <div class="middle">middle</div>

      <!-- <div class="after"></div> -->
    </div>
    <!-- 任何div至少包含两个隐形div 分别叫before after-->
    <!-- 位置：紧贴上下两半标签  默认是行内元素 无内容-->
    <ul>
      <li>1</li>
      <li>2</li>
      <li>3</li>
    </ul>

    <style>
      ul {
        list-style: none;
        /* width: 200px; */
      }
      li::before {
        content: "#";
      }
      li::after{
        content: "";
        background-image: url('/filtertestss.png');
        /* background-color: red; */
        display: block;
        width: 20px;
        height: 20px;
        background-size: contain;
      }
      .simple {
        width: 100px;
        height: 60px;
        background-color: goldenrod;
      }
      .simple ::before {
        width: 10px;
        height: 20px;
        background-color: cornflowerblue;
        content: "dss";
      }
      .middle {
        width: 80px;
        height: 40px;
        background-color: blue;
      }
    </style>
  </body>
</html>
